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Reply to "1915cc carburetor set up"

@Sacto Mitch posted:

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OK, spark scatter.

If your distributor is doing what distributors ought to, it goes ‘spark’ every time the crank comes around to ‘x’ degrees before TDC. ‘X’ will vary with what the rpm’s are, but AT ANY GIVEN rpm, the spark should be at exactly the same timing for every revolution of the crank.

The cool thing is that you can actually SEE this with a timing light. As you slowly advance the rpm’s from idle, the image you see of the timing mark will slowly advance across the degree scale until it stops moving at max advance.

If the mark starts jumping around or even disappears, the spark is happening at different times (or maybe not at all) for each turn of the crank. This is a guaranteed way to make an engine run like crap, and it must be fixed before you have any chance of getting the carbs dialed in.

It could be the carbs are already dialed in. You’ll just never know until you verify that the spark is sparking when it should - up and down the rev range, not just at idle or max advance.

How do you fix spark scatter?

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